The present invention relates to a drill bit with an exchangeable cutting portion.
The term “drill bit” includes all drilling tools having a hollow cylindrical drill shaft and a cutting portion with one or more cutting elements, for example, core drill bits and socket drill bits. Depending on the intended application, the drill bits may additionally have elements, for example, a depth stop, which limits the drilling depth.
Drill bits consist of a cutting portion with one or more cutting elements, a drill shaft portion and a receiving portion with an insertion end. The drill bit is mounted in the tool receptacle of a core drilling device via the insertion end and is driven during drilling operation by the core drilling device in a direction of rotation about the axis of rotation. Known drill bits are subdivided into drill bits with an exchangeable cutting portion and drill bits without an exchangeable cutting portion, and a distinction is made between releasable and nonreleasable connections in the case of the drill bits with an exchangeable cutting portion. A connection is referred to as releasable if the connection can be released by the user without destruction, such as, for example, a plug connection, a screw connection or a magnetic connection. A connection is referred to as nonreleasable if the user can release the connection only by destroying it such as, for example, a soldered connection, a welded connection, a riveted connection or an adhesively bonded connection.
With the drill bit disclosed in U.S. Pat. No. 3,888,320 A, the cutting portion and the drill shaft portion are connected to one another by a releasable plug-twist connection. The cutting portion comprises an annular portion, which is connected at a first end to a plurality of cutting elements and has an outer insertion element and an annular stop shoulder at a second end. The drill shaft portion comprises a cylindrical drill shaft which has an inner insertion element and an end face on an end facing the cutting portion. The insertion elements form a plug connection in a plug-in direction parallel to the axis of rotation. The outer insertion element has a plurality of pin elements on the inside, these pin elements being directed radially inward in a plane perpendicular to the axis of rotation. The inner insertion element has a plurality of slot-shaped recesses in an L shape into which the pin elements are inserted. The L-shaped recesses consist of a cross-slot running perpendicular to the axis of rotation and a connecting slot running parallel to the axis of rotation and connecting the cross-slot to a lower edge of the inner insertion element.
With the known drill bits with exchangeable cutting portions, there is an axial clearance between the cutting portion and the drill shaft portion in one direction when the plug-rotational connection is closed. A clearance is formed between the end face of the inner insertion element and the stop shoulder of the outer insertion element so that the transfer of force from the drill shaft portion to the cutting portion takes place exclusively by way of the pin elements. The clearance also results in the fact that a cooling and rinsing medium is not conveyed completely to the working site but instead can be misguided into the clearance on the inside of the drill bit.
Another disadvantage of the known drill with an exchangeable cutting portion is manifested when the drill bit becomes jammed in the substrate. In the case of drill bits, it often happens that the drill bit becomes jammed in the substrate while drilling and must be released by the operator. To release the jammed drill bit, in the case of stand-guided core drilling devices, the drill bit must be driven in the opposite direction of rotation and a tractive force directed in the direction opposite the drilling direction must be exerted on the drill bit by the drill stand. The operator attempts to free the drill bit from the substrate by manually turning it with the help of a wrench and at the same time pulling with the help of the drill stand. In the case of the L-shaped recesses, there is the risk that the operator might rotate the drill shaft portion about the axis of rotation until the pin element comes to a stop on the connecting slot while at the same time operating the hand wheel on the drill stand, so that the pin element is moved out of the connecting slot. As soon as the plug-twist connection between the cutting portion and the drill shaft portion has been released, the cutting portion must be freed from the substrate in some other way, for example, by removal of the substrate.
The object of the present invention is to develop a drill bit having a replaceable cutting portion with which the stability in drilling and the durability with respect to a tensile load are increased by a drill stand. Furthermore, this should reduce the risk that the plug-twist connection might be opened unintentionally while removing a jammed drill bit from the substrate and the drill shaft portion might be removed from the substrate without the cutting portion.
It is provided according to the invention that the at least one pin element is fastened onto an outer side of the inner insertion element and the outer insertion element has the at least one slot-shaped recess. Then the plug connection and the twist connection of the insertion elements can be closed one after the other or simultaneously.
The plug-twist connection of the insertion elements according to the invention improves the stability and durability of the drill bit with respect to tensile loads. The drill bit portion having the slot-shaped recesses is more susceptible to deformation due to tensile loads than is the drill bit portion to which the pin elements are attached. The arrangement of the slot-shaped recesses on the exchangeable cutting portion has the advantage that the less stable of the two drill bit portions is replaced regularly. The risk of deformation due to tensile loads increases with an increase in the proportion of slot-shaped recesses on the circumference of the insertion element. Since the diameter of the outer insertion element is larger than the diameter of the inner insertion element, more circumference is available for the slot-shaped recesses on the outer insertion element and/or the proportion of recesses on the circumference is lower. The drill bit is more stable when the slot-shaped recesses are provided on the outer insertion element.
Due to the arrangement of the pin elements on the inner insertion element and the arrangement of the slot-shaped recesses on the outer insertion element, the drill bit may be designed to be dense on the inside and the misdirection of a cooling and rinsing medium can be prevented. The cooling and rinsing medium supplied through the insertion end of the drill bit, for example, flows completely past the processing site in the case of a dense drill bit and ensures cooling of the cutting elements and removal of drilling cuttings. The drill bit according to the invention also makes it possible for the operator to monitor the opening and closing of the plug-twist connection. Such monitoring is impossible or can be done only to a limited extent when the slot-shaped recesses are provided on the inner insertion element.
In a preferred embodiment the end face of the inner insertion element in the connected state is in contact with the stop shoulder of the outer insertion element. The transfer of force from the drill shaft portion to the cutting portion takes place via the end face and the stop shoulder in drilling. The risk of deformation of the outer insertion element is reduced when the transfer of force does not take place via the pin elements, so that the drill bit according to the invention has a greater stability. The stop shoulder may be designed to be in the shape of a ring or in the form of an annular portion. Due to flat support of the end face on an annular stop shoulder, the drill bit is designed to be dense on the inside, so that misdirection of the cooling and rinsing medium is prevented. The cooling and rinsing medium supplied via the insertion end of the drill bit, for example, flows completely past the working site and ensures cooling of the cutting elements and removal of drilling fines.
The length of the inner insertion element is especially preferably greater than the length of the outer insertion element. Due to the difference in length between the inner and outer insertion elements, this ensures that the end face of the inner insertion element is in contact with the stop shoulder of the outer insertion element and that there is a defined transfer of force from the drill shaft portion to the cutting portion during drilling.
The length of the outer insertion element especially preferably amounts to at least 18 mm. At a minimum length of 18 mm for the outer insertion element, an adequate durability of the cutting portion is ensured. The slot-shaped recesses can be positioned on the outer insertion element at a height, such that the cutting portion is resistant to the resulting tensile stresses in releasing a jammed drill bit with the help of a drill stand.
The length of the outer insertion element is especially preferably no greater than 28 mm. Up to a length of 28 mm for the outer insertion element, the durability of the cutting portion with respect to tensile loads is improved. Greater lengths for the outer insertion element have little or no influence on the durability of the cutting portion with respect to a tensile load and result only in an increased cost of materials and increased processing.
In a preferred embodiment, the outer and inner insertion elements are designed in the form of a ring, wherein the difference between an inside diameter of the outer insertion element and an outside diameter of the inner insertion element is greater than 0.11 mm. Due to the clearance formed between the outer and inner insertion elements, this ensures that the end face of the inner insertion element comes to rest against the stop shoulder of the outer insertion element. The drill bit is designed to be tight on the inside, so that the supply of a liquid or gaseous cooling and rinsing medium to the cutting elements is ensured. Furthermore, there is a defined transfer of force from the core drilling device to the end face of the drill shaft portion and then to the stop shoulder of the cutting portion.
In a preferred embodiment of the drill bit, three or more pin elements are attached to the outside of the inner insertion element, and the outer insertion element has three or more slot-shaped recesses, such that the number of recesses is greater than or equal to the number of pin elements. With the drill bit according to the invention the transfer of force from the end face of the inner insertion element to the stop shoulder of the outer insertion element and the transfer of torque take place via the pin elements to the outer insertion element. The pin elements here are especially preferably distributed uniformly around the axis of rotation of the drill bit. Due to the uniform distribution of the pin elements, there is no assignment of the pin elements to the recesses, so a pin element may be inserted into each recess.
The number of slot-shaped recesses must be greater than or equal to the number of pin elements. For closing the plug and twist connection, a slot-shaped recess must be provided for each pin element. The design of a drill bit on which the number of recesses is greater than the number of pin elements has the disadvantage that the stability of the cutting portion is unnecessarily reduced. This design is suitable if at all for drill bits with very large diameters, because with these drill bits, the proportion of the recesses on the circumference of the outer insertion element is lower than with drill bits having smaller diameter.
Six pin elements are especially preferably provided on the outside of the inner insertion element, and the outer insertion element has six or more slot-shaped recesses. A twist connection with six pin elements, each having a pin diameter of 6 mm, is suitable for transfer of torque for drill bits with different diameters, for example, 50 mm to 250 mm.
In a preferred embodiment of the drill bit the pin elements have a pin height perpendicular to the axis of rotation such that the pin height amounts to between 68% and 89% of the shaft width of the drill shaft. The width of the inner insertion element is preferably approx. 50% of the width of the drill shaft. With an increase in pin height, the area for transfer of torque is increased. Furthermore, the durability with respect to tensile loads is improved.
The pin elements are especially preferably designed as circular cylinders with a pin radius such that the pin radius is between 2.5 and 5 mm. The transfer of torque from the drill shaft portion to the cutting portion takes place by way of the pin elements and the outer insertion element. The greater the pin radius of the pin elements, the smaller the number of pin elements required for the transfer of torque.
In a preferred embodiment, the slot-shaped recesses have a cross slot perpendicular to the axis of rotation such that the cross-slot is connected by a connecting slot to an upper edge of the outer insertion element. The outer insertion element is designed to be open in the region of the connection slots. The pin elements are inserted through the connecting slot such that the connecting slot may be arranged parallel or obliquely to the axis of rotation. The transfer of torque from the pin element to the outer insertion element takes place in the cross-slot.
The cross-slot preferably has a lower distance from the annular portion of at least 3 mm parallel to the axis of rotation. A minimum distance of 3 mm ensures adequate durability of the cutting portion with respect to a tensile load in releasing a jammed drill bit with the help of a drill stand.
The lower distance of the cross-slot from the annular portion is especially preferably no greater than 5 mm. Up to a distance of 5 mm, the durability of the cutting portion with respect to tensile loads is improved. Greater distances have little or no effect on the durability of the cutting portion with respect to a tensile load and lead only to increased cost of materials and processing.
In a refinement of the drill bit, the cross-slot has a follower region and securing region, wherein the follower region is connected to the connecting slot on a side of the connecting slot that faces the direction of rotation, and the securing region is connected to the connecting slot on a side of the connecting slot facing away from the direction of rotation. The transfer of torque from the drill bit portion to the cutting portion takes place by way of the pin element and the follower region. The securing region is arranged on the side of the connecting slot opposite the follower region. The securing region reduces the risk that in releasing a jammed drill bit from the substrate, the plug-twist connection between the drill shaft portion and the cutting portion might be unintentionally opened. The operator attempts to free the jammed drill bit from the substrate by turning the drill shaft portion with the help of a wrench about the axis of rotation and at the same time pulling on it with the help of the drill stand. Practice has shown that operator will pull on the drill shaft portion primarily when the pin element is stopped against the cross-slot. If the pin element in the drill bit according to the invention is stopped on the follower region or on the securing region, there is no risk that the plug-twist connection will be opened. In the case of the drill bit according to the invention, the plug-twist connection is opened only when the operator pulls on the drill shaft portion precisely at the moment when the pin element is above the connecting slot. The risk that the plug-twist connection will open unintentionally is greatly reduced in comparison with slot-shaped recesses in an L shape.
The width of the follower region is preferably no less than the pin radius plus 1.5 mm. With this minimum width for the follower region, a sufficient durability of the cutting portion with respect to a tensile load is ensured by a drill stand. The pin elements are in contact with the follower region and do not break out of the follower region.
The width of the follower region is especially preferably no greater than the pin radius plus 3 mm. Up to a width equal to half the pin diameter plus 3 mm, the durability of the cutting portion with respect to a tensile load is improved by a drill stand. Greater widths have little or no influence on the durability of the cutting portion with respect to a tensile load and reduce the stability of the cutting portion unnecessarily.
In a first preferred variant, the width of the follower region and the width of the securing region are the same. The follower region and the securing region have a minimum width of pin radius plus 1.5 mm. This embodiment is recommended in particular for drill bits having large diameters in which the proportion of cross-slots on the circumference is low.
In a second preferred variant, the width of the follower region is greater than the width of the securing region. The follower region and the securing region have a minimum width of pin radius plus 1.5 mm. This embodiment is recommended in particular for drill bits having a small diameter, in which the proportion of cross-slots on the circumference is high.
The height of the connecting slot parallel to the axis of rotation is preferably at least 10 mm. At a height of at least 10 mm, a sufficient durability of the cutting portion with respect to a tensile load is ensured by a drill stand.
The height of the connecting slot parallel to the axis of rotation is especially preferably no greater than 13 mm. Up to a height of 13 mm, the durability of the cutting portion with respect to a tensile load is improved by a drill stand. Greater heights have little or no influence on the durability of the cutting portion with respect to a tensile load due to a drill stand and lead only to increased cost of materials and processing.
In a refinement of the drill bit, the annular portion has a guide portion, wherein the guide portion is in flush contact with an outer edge, an inner edge or an outer and inner edge of the cutting elements parallel to the longitudinal axis. Due to the flush contact of the guide portion with the cutting elements, the guide portion forms a guide for the cutting elements during drilling and thereby stabilizes the cutting elements. The guide may be on the outside of the drill bit over the substrate surrounding the borehole or on the inside of the drill bit over the drill core.
The length of the guide portion parallel to the longitudinal axis is preferably less than 4 mm. A guide portion which is smaller than 4 mm would not interfere much or at all with the supply of a cooling and rinsing medium.
In a preferred embodiment of the drill bit, a lug is arranged on the outside of the inner insertion element, and the outer insertion element has a groove, such that the lug and the groove in the connected state form a form-fitting connection in the axial direction. Due to the additional form-fitting connection between the drill shaft portion and the cutting portion, it is possible to further reduce the risk that the releasable connection between the drill shaft portion and the cutting portion will unintentionally open on removal of a jammed drill bit from the substrate. The design of the form-fitting connecting means as a lug and groove allows a simple and reliable connection which makes it difficult to remove the drill shaft portion from the cutting portion. The holding force of the connection can be adapted to the field of use of the drill bit by way of the geometry of the lug and the groove.
The lug is preferably arranged between the pin elements and the drill shaft in the axial direction, and the groove is arranged at the level of the slot-shaped recesses in the axial direction. Sections having a resilient effect are formed between the slot-shaped recesses of the outer insertion element. The elastic effect can be adjusted by means of the number and the axial height of the slot-shaped recesses and the length of the outer insertion element. To separate the drill shaft portion from the cutting portion, a force is exerted on the end face of the outer insertion element in the axial direction with the help of a tool. Due to the action of the force, the elastic section of the outer insertion element is deflected and the form-fitting connection between the lug and the groove can be released. The greater the distance from the groove to the stop shoulder of the outer insertion element, the greater is the deflection of the elastic section. The groove is especially preferably designed in the form of a ring and is arranged in a plane perpendicular to the axis of rotation. A groove designed in the form of a ring, which is itself arranged at the level of the slot-shaped recesses, supports the elastic effect of the sections of the outer insertion element between the slot-shaped recesses.
The axial direction is defined as a direction parallel to the axis of rotation of the drill bit. In the connected state of the drill bit portions, the axis of rotation of the drill bit coincides with the longitudinal axes of the drill bit portions, the cutting portion and the drill shaft portion. The radial plane is defined as a plane perpendicular to the axis of rotation, and a radial direction is defined as a direction running in the radial plane and intersecting the axis of rotation of the drill bit and/or the longitudinal axis of the drill bit portions.
Exemplary embodiments of the invention are described below with reference to the drawings. These should not necessarily represent the exemplary embodiments drawn to scale and instead the drawings are done in the form of schematic diagrams or in a slightly distorted form wherever this serves the purpose of illustration. With regard to supplemental features from teachings that are directly recognizable from the drawings, reference is made to the relevant prior art. It should be recalled that a variety of modifications and changes can be made with respect to the shape and the detail of an embodiment without deviating from the general idea of the invention. The features of the invention disclosed in the description, the drawings and the claims may be essential to the refinement of the invention either individually or in any combination. Furthermore, any combinations of at least two of the features disclosed in the description, the drawings and/or the claims fall within the scope of the invention. The general idea of the invention is not limited to the precise form or detail of the preferred embodiment that is described and illustrated below nor is it limited to an object that would be restricted in comparison with the object claimed in the claims. With given ranges of dimensions, values within the aforementioned limits should also be disclosed as limit values and may be usable in any way and may also be claimable. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or for parts with identical or similar functions.